This invention relates generally to airfoil blades, and, more particularly, this invention relates to an automated airfoil blade qualification system and method.
Aircraft engine compressor blades are manufactured to stringent airfoil tolerances, and all blades must pass a qualification process in which dimensions are checked and, if necessary, are manually brought into compliance. Dimensions of primary interest are section contours, twist, and bow. The qualification process is time-consuming and requires highly skilled labor. In many instances, blades are still deformed by hand. The process adds significantly to the overall manufacturing cost of compressor blades.
Shot peening is used to increase fatigue strength, to relieve tensile stresses that contribute to stress-corrosion cracking, to form and straighten metal parts. In shot peening, spheroidal particles of cast steel, cast iron, glass, etc., are blown or mechanically impelled in a high velocity stream or gravity dropped against the surface to be treated. The individual shot particles produce shallow, rounded overlapping dimples in the surface, stretching it radially from each point of impact and causing cold working and plastic flow. The degree of peening, or peening intensity which may be expressed in terms of Almen arc height, is a function of the weight, size, hardness, and velocity of the peening particles, exposure time, type of substrate, angle of impingement, and various other factors. Shot peening of airfoil blades is capable of producing gentle curvatures in the blades. Shot size selection, intensity, and coverage levels as required to obtain the desired contour may be permitted. Shot size selection depends on type of material, thickness, amount of curvature, and roughness requirements. A highly tapered material may require several shot sizes although this complicates peening machine design.
Laser shock peening or laser shock processing, as it is also referred to, is a process for producing a region of deep compressive residual stresses imparted by laser shock peening a surface area of a workpiece. Laser shock peening typically uses multiple radiation pulses from high power pulsed lasers to produce shock waves on the surface of a workpiece. Laser shock peening, as understood in the art and as used herein, means utilizing a laser beam from a laser beam source to produce a strong localized compressive force on a portion of a surface by producing an explosive force by instantaneous ablation or vaporization of a painted or coated or uncoated surface.
Laser forming is another process for affecting material without hard tooling and with acceptable material degradation levels. Laser forming is a process in which material forming is caused by temperature gradients and thermal stresses produced by absorption of power from a scanning laser beam. Laser forming requires no tooling and has the ability to flatten or adjust parts in a controlled manner. Laser forming originated from the process of flame bending or line heating which uses an oxy-acetylene torch as the heat source. The diffuse nature of the flame makes the process difficult and success relies heavily on operator skill, especially to establish a steep temperature gradient in thin sections and materials with a high thermal conductivity. Most flame bending uses a localized thermal upsetting mechanism. The heating rate can be high when a laser beam irradiates a metallic workpiece and steep thermal gradients are easily achieved. The laser beam creates a very narrow thermal deposition profile in comparison with flame, and has precise power control enabling more exact and detailed geometry to be formed in a repeatable manner.